Methanol oxidation on Ru(0001) for direct methanol fuel cells: Analysis of the competitive reaction mechanism

The competitive oxidation reaction mechanism of methanol on the Ru(0001) surface has been investigated by periodic density functional theory (DFT). Stable adsorption configurations, elementary reaction energies and barriers, the potential energy surface (PES), and the electrochemical potential analysis were elucidated. The results showed that O-H bond activation was more competitive than C-H and C-O bond activation during the initial methanol oxidation. Competitive pathways occurred for CH₃OH oxidation to CH₂O via CH₃OH → CH₃O → CH₂O versus CH₃OH → CH₂OH → CH₂O, further to COOH via the CO pathway CH₂O → CHO → CO → COOH versus the non-CO pathway CH₂O → CH₂OOH → CHOOH → COOH, and finally oxidation to CO₂. Taking PES and the electrochemical potential analysis into account, CH₃OH → CH₂OH → CH₂O → CH₂OOH → CHOOH → COOH → CO₂ appeared to be the preferred oxidation pathway. The OH group could inhibit CO formation by directly reacting with CH₂O to yield CH₂OOH but could not efficiently remove the CO that had already been produced by the reactions.